The present invention relates to a fuel cell system having an ejector which combines a new gas to be supplied to a fuel cell with a gas discharged from the fuel cell and supplies the combined gas to the fuel cell.
In a known conventional example of this type of fuel cell system, the ejector is constituted to be capable of varying a gas flow rate so that the gas can be supplied in accordance with the load of the fuel cell. For example, a fuel cell system described in Japanese Patent Laid-open Publication No.2002-56870 (pages 4 to 6, FIG. 2) includes two ejectors corresponding to predetermined hydrogen gas flow rates, and the two ejectors are switched arbitrarily by an actuator based on the output current of the fuel cell. In a fuel cell system described in Japanese Patent Laid-open Publication No.H9-213353 (page 3 and FIG. 1), the opening of a fuel supply valve of the ejector is adjusted arbitrarily on the basis of the detection results of a plurality of pressure or flow rate sensors disposed in a hydrogen gas supply system.
However, with this type of conventional fuel cell system, an actuator or sensor is provided to vary the flow rate using the ejector, and hence control of the entire system becomes complicated. The controllability (resolution) of the actuator and so on may be increased to solve this problem, but this may lead to a cost increase.